Sputter coating is a process carried out in a vacuum chamber which is filled with a generally chemically inert gas in which a substrate is coated with a material from a target of sputtering material subjected to a negative electrical potential with respect to the chamber wall or other anode. The potential gradient adjacent the target surface causes electrons to be emitted from the target which, on their way to the chamber anode which is usually formed in part by the grounded chamber wall, strike and ionize some the inert gas. The positive ions formed are then attracted to the negative target which they strike, transferring momentum to the target material, and ejecting particles of the material from the target surface. The substrate to be coated, which is positioned in the chamber usually with its surface facing the target, receives some of the ejected particles which adhere to and coat the substrate surface.
Magnetron sputtering is a sputter coating process in which a magnetic field is formed over the target surface, usually including magnetic field lines parallel to the target surface, and, in many applications, in the form of a closed magnetic tunnel. The magnetic field causes the electrons emitted to move in curved spiral paths which trap them in regions proximate the target surface enclosed by the field, thereby increasing the rate of electron collisions with gas atoms, which in turn increase the ionization of the gas and the efficiency of the sputtering process.
In magnetron sputter coating processes, the sputtering of materials from the sputtering target occurs most rapidly into regions of the target where the plasma trapped by the magnetic field is the most dense. This causes the proportionate consumption or erosion of the sputtering material from the target surface. The erosion of sputtering material from other portions of the sputtering target surface generally occurs at a rate which varies in proportion to the strength and/or duration of the plasma over that portion of the target surface. Such erosion of the target at different rates across the target surface is sometimes desirable to achieve, for example, uniform coating of the substrate, as for example is described in the commonly assigned U.S. Patent No. 4,957,605, hereby expressly incorporated herein by reference.
The shape of a sputtering target as well as its composition determine the operating parameters of the sputtering machine, such as the sputtering power levels, the characteristics of the magnetic fields over the target, the gas composition and pressure within the sputtering chamber, the sputtering process time, and other factors, to which the machine must be set for operation. The shape of the sputtering target varies with the use of the target as the target erodes. The history of the use of the target and of the parameter settings over the course of the history of the target affect the characteristics of the target, including particularly its shape, at any point in the life of the target. Thus, parameter settings for optimal use of the target at any point in time will vary with the history of the use of the particular target. In addition, variations from target to target, such as variations in composition, texture or crystal structure, may require different adjustments in operating parameters of the machine for optimal performance of the sputter coating process. Such adjustments will be experienced as the target is used. Furthermore, the identity of the particular target and information regarding its composition and history of use will, in some cases, be important in evaluating the coated products produced with the sputtering target at any point in its life. This is particularly important when targets are replaced and when targets which have been previously used are installed in a sputtering machine. The use of information regarding the parameters associated with the sputtering process, are discussed in the commonly assigned and copending U.S. patent application Ser. No. 07/570,943, filed Aug. 22, 1990, now U.S. Pat. No. 5,126,028 entitled "Sputter Coating Process Control Method and Apparatus", hereby expressly incorporated herein by reference.
The use of information regarding the identity, characteristics and history of the sputtering target, and the correlation of that information with the products produced by the target has, in the prior art, been a manual process. Similarly, proper settings of the operating parameters of the machine have required manual decision making by the machine operator. Accordingly, the prior art has provide inadequate utilization of information regarding the target, and has provided inefficiency and a risk of error.
Accordingly, there is a need to provide a method and apparatus for effectively maintaining and utilizing information regarding the sputtering target in a sputter coating process.